1. Field of the Invention
The invention relates to a wet friction lining with a textile fabric, which is displaced with a resin or resin mixture, a friction component with a substrate on which a wet friction lining is disposed, and a method of producing a friction lining for wet operation, whereby a textile fabric is displaced with a resin or resin mixture and then cured under pressure and/or high temperature.
2. Prior Art
Conventional friction linings for wet operation are usually made from what are referred to as roving fabrics with long fibers, for which purpose different fabric weaves such as for example canvas binding, Atlas binding, twill binding, etc., are used. These fabrics are impregnated with resin and cured at a defined pressure and temperature during the subsequent processing step in order to obtain a specific strength. The greater the amount of resin which can be incorporated in the lining, the greater the strength of the friction lining will be. The materials currently used contain a proportion of resin which is limited to between 18% and 40%. There are various reasons for this. Firstly, the porosity of the fabric and hence the ability to absorb oil is reduced by the resin. This leads to a reduction in the cooling capacity of the friction system and impairs resistance to galling. Secondly, the pressing operation causes a resin film to form at the surface, which leads to fluctuating friction values and also drastically reduces the coefficient of friction. The resin at the surface often also leads to a higher noise level. A low proportion of resin increases the wear rate and results in a shorter service life due to disintegration.
Many types of friction linings are already known from the prior art. For example, patent specification DE 31 17 823 A describes a method of producing friction linings for friction clutches, whereby strands containing textile fibers, binding agent and lining materials are wound to form an annular disc, this disc is dried, hot-pressed and cured, after which its surfaces are smoothed by a machining process. The binding agent and lining materials are mixed with staple fibers to form a homogeneous mixture, which is then pressed to form one or more strands from which the disc is then wound directly. The length of the staple fibers is approximately 6 mm.
Patent specification DE 29 44 864 A also describes a friction lining, essentially containing a fiber material, a polymeric binding agent compound, fillers and optionally other additives, and the fiber material is made up entirely or partially of silicic acid fibers. The silicic acid fibers may have a staple length of from 1 mm to 40 mm. The fiber material may also be made up of a mixture of silicic acid fibers and carbon fibers. The silicic acid fibers may be twisted with fully aromatic polyamide fibers in a ratio by volume of 1:1 to form a composite thread. Several of these threads are assembled to form a strip, which is fed through an immersion bath containing a standard impregnating mixture. This mixture essentially contains phenolic resin, natural and synthetic sizing agent, as well as carbon black and graphite, kaolin, zinc oxide and sulfur. Having been impregnated, the strips are dried until they are no longer sticky and are then wound to form a disc-shaped preform and then pressed. Amongst other things, this friction lining is used for disc and drum brakes, as friction lining for clutches and as a disc material in multiple-disc clutches.
Patent specification DE 30 23 188 A describes a material for producing a friction element with improved abrasion resistance, comprising a mixture of approximately 5% to 60% of aramide fibers coated with 40% to 95% of a heat-curable cement incorporating a heat-cured resin and a heat-cured elastomer. The heat-curable cement may contain 20% by weight to 80% by weight of phenolic/formaldehyde resin and 80% to 20% of natural rubber. The aramide fibers may be continuous threads, staple fibers or cut fibers. This being the case, the aramide fibers may be coated with the heat-curable cement so that the fiber bundle is prized open or opened up to allow the cement dispersion to penetrate more easily, enabling all the threads to come into contact with the cement and absorb cement solids across their entire length.
Patent specification DD 224 641 A describes a method of producing friction materials containing glass fibers as a reinforcing agent and rubber as a binding agent, whereby the friction material is vulcanized in the semi-ebonite range, in other words with more than 5% by weight and less than 25% by of sulfur by reference to the rubber content of the friction material. The friction material may contain short fibers, such as staple fibers, mill fibers, short-cut fibers or similar, which are admixed with rubber in a solid, dissolved or dispersed form in mixing machines, and with the fillers and vulcanizing agent and other agents, for example.
These known friction linings are used for dry applications, for which purpose the fibers and resin are brought to a homogeneous mixture and then processed to form a strand.